Concrete submerged for 67-yr in seawater has shown that low permeability concrete is highly durable to sulfate attack; however, more permeable concrete is susceptible to sulfate attack. Large concrete blocks were retrieved off the Los Angeles Harbor breakwater. Concrete blocks of size 69 in. x 69 in. x 42 in. which were retrieved were part of a test program initiated by the Corps of Engineers in 1905. Cores were tested for compressive strength and material deterioration to determine if the concrete was attacked by seawater. Results from other reports of sulfate attack on concrete are summarized. It is concluded that for long-time durability of concrete exposed to seawater, a reduced permeability and reduced alkalinity of concrete appear to be as important as low 3 Ca.Al2O3 content of cement.